Interpretive Summary: The impact of removing corn residue on soil quality and productivity is of concern to producers. In order to determine the short and long term effects of removing corn residue on soil quality indicators such as soil C, a field study was established in eastern South Dakota in 2000 using no-till soil management within a two-year corn/soybean rotation with and without cover crops consisting of slender wheatgrass in corn and lentils in soybeans. Our specific research objective was to examine the effects of three residue removal treatments of low, medium, and high on soil quality characteristics and to determine if cover crops improve soil quality characteristics within the three residue removal treatments. This research is being conducted as part of a collaborative national effort with the U.S. Department of Agriculture and academia throughout the United States to determine the feasibility and sustainability of the practice of removing corn residue for biofuels production. Overall, the data suggest that the soil properties indicative of soil quality are negatively impacted by removal of corn residue and that long term pools of soil C are being depleted when residue is removed. Cover crops increase some pools of soil C that are useful for improving or maintaining soil quality.

Technical Abstract:
Corn [Zea mays L.] residue is being considered as a feedstock source for biofuels production. The impact of removing corn residue on soil productivity needs to be determined in order to preserve the soil resource. A corn-soybean [Glycine max (L.) Merrill] rotation was established in 2000 and the effect of removing corn residue at three rates (37, 55, and 98%) on several soil carbon (C) pools in the 0-5 cm layer of soil was determined after four rotational cycles (8 years). The effect of cover crops (slender wheatgrass [Agropyron caninum (L.) Beauv.] in corn and lentil [Lentilla lens var. Morton] in soybeans) presence or absence on soil C pools was also measured. As the rate of residue removal increased, soil organic matter (SOM), wet aggregate stability (WAS), and C:N decreased significantly. There was a significant decrease in microbial activity by fluorescein diacetate analysis for plots that were previously planted to corn. Although the effect was not significant, there was a decrease in soil C as the rate of removal increased. In addition, soil was analyzed by 13C NMR and the spectra for the high rate of residue removal contained an abundance of aromatic C structures. This means that the soil was depleted in fresh residue and less humified pools of soil C are not being replenished. The humin fraction had a reduction in %C under the medium and high rates of residue removal without a cover crop and is likely beginning to be depleted. Glomalin related soil protein and immunoreactive soil protein were higher in soils with cover crops, likely due to increased plant diversity and extending the growing season to allocate more C belowground. Overall, the data suggest that the soil properties indicative of soil quality are negatively impacted by removal of corn residue.